Rotor balancing system for turbomachinery

ABSTRACT

The present invention relates to an improved rotor balancing system which allows for fine tune onsite adjustment for turbomachinery. The rotor balancing system comprises a rotor element having a row of locating slots and a device for reducing windage effects caused by the locating slots and protruding anti-rotation pins. In a preferred embodiment, the device for reducing windage effects comprises at least one balancing ring which partially or fully covers the locating slots and internal slots for engaging and.disengaging that does not protrude outbound of the ring. Each balancing ring is preferably provided with two integrally formed anti-rotation members for engaging the locating slots. Each balancing ring is also preferably provided with a slot in a weighted portion of the ring for receiving a tool for positioning the balancing ring in a desired position. A method for positioning the balancing ring on a rotor element using the slot and the tool is also described herein.

BACKGROUND OF THE INVENTION

The present invention relates to a rotor balancing system forturbomachinery which safely secures balancing rings to a rotor elementwhile reducing windage effects caused by locating slots on the rotorelement and to a method for positioning a balancing ring on a rotorelement.

In rotating machinery, it sometimes becomes necessary to trim thebalance of one of the rotor elements after the machinery has beeninitially balanced for assembly and has been operating in service.Typically, the machinery must be disassembled, completely or partially,to permit rebalancing or trim balancing of the offending rotor element.With aircraft gas turbine engines, it is desirable to be able to quicklyand easily trim balance a compressor rotor after an airfoil has sufferedforeign object damage and the damaged blade or blades have been blendedin without removal of the engine from an aircraft.

It is known in the prior art to provide a construction for trimbalancing a rotating piece of machinery which construction includes anannular rotor element having an outer face and an inner circumference,locating slots around the inner circumference of the rotor element, atleast one annular groove within the rotor element behind the rotorelement face, balance ring means positioned in the at least one annulargroove, which balance ring means is split and has a weighted mass at oneend thereof, and tab means connected by pin means to the balance ringmeans at the weighted mass end, which pin means extends through therotor element locating slots, and the tab means being mounted on the pinmeans so as to be external of the rotor element. The construction alsoincludes a casing structure means associated with the rotor element,which casing structure means has an opening therein through which toolmeans may be inserted to contact the tab means and deflect the pin meansinward a controlled distance to free the pin means from the locatingslots and permit a circumferential relocating of the balance ring means.Such a trim balancing construction is illustrated in U.S. Pat. No.5,167,167 to Tiernan, Jr. et al.

One of the deficiencies of the Tiernan, Jr. et al. construction is thatthe locating slots act similar to rotating blades, turning and heatingup the air in the cavities as the rotor element rotates. As a result,heated air is injected into the flow path. The mixture of hot cavity airand cooler flow path air reduces the overall fan efficiency.Additionally, the air pumping (windage) caused by the locating slotsforces more air into the flow path. The air impinges with engine coreflow reducing overall engine air flow. In addition the locating pinincreases windage since it protrudes outboard of the balance ring andacts as a paddle turning air. Subsequently, this adds to the reductionin engine air flow.

Another deficiency in the present design is the ability to fine tuneadjust the rotor trim balance. The anti-rotation pin slop and large diskengagement slot decrease the trim balance fine tune adjustment.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a rotorbalancing system which reduces windage effects caused by rotor elementcomponents.

It is a further object of the present invention to provide a rotorbalancing system as above having at least one counterweight balancingring which substantially eliminates air cavity pumping (windage) causedby locating slots machined into a turbomachinery rotor.

It is a further object of the present invention to provide a rotorbalancing system as above which has an integral structure for securingthe counterweight balancing rings to the rotor element.

It is yet another object of the present invention to provide an improvedmethod for positioning a counterweight balancing ring on a rotorelement.

The foregoing objects are achieved by the rotor balancing system and themethod of the present invention.

In accordance with the present invention, a rotor balancing system forturbomachinery comprises a rotor element having a row of locating slotsand means for reducing windage effects caused by the locating slots. Thewindage reducing means comprises at least one balancing ring secured tothe rotor element which at least partially covers said locating slots toreduce windage effects.

In another aspect of the present invention, each balancing ring isprovided with anti-rotation means for securing it to the rotor element.The anti-rotation means in a preferred construction comprises twointegrally formed anti-rotation members for engaging two locating slotson the rotor element.

In yet another aspect of the present invention, each balancing ring isprovided with a slot machined into its weighted end. When a tool isplaced in the slot and pushed radially inboard, the balancing ring canhave its anti-rotation members disengaged from the locating slots andcan be rotated to a new position.

In still another aspect of the present invention, a method forpositioning a balancing ring on a rotor element is provided. The methodcomprises providing a rotor element having a row of locating slots andat least one interior annular groove, inserting into the at least oneinterior annular groove at least one split balancing ring having aweighted end, a slot machined into the weighted end, and means forengaging the locating slots in the rotor element, and inserting the toolinto the slot in the weighted end of the at least one balancing ring todisengage the at least one balancing ring from the rotor element androtate the at least one balancing ring to a balance position.

The rotor balancing system of the present invention adds more diskengagement slots on the disk and an integral anti-rotation pin designsized closely to the disk slot. The result is more capability for finetuning the trim balance.

Other details of the rotor balancing system and the method of thepresent invention, as well as other objects and advantages attendantthereto, are set forth in the following detailed description and theaccompanying drawings in which like reference numerals depict likeelements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a rotor element having scalloped shapedlocating slots;

FIG. 2 is a sectional view of the rotor element of FIG. 1;

FIG. 3 is a front view of a front counterweight balancing ring to bemounted to the rotor element of FIG. 1;

FIG. 4 is a rear view of the counterweight balancing ring of FIG. 3showing the integrally formed means for engaging the locating slots;

FIG. 5 is a front view of a rear counterweight balancing ring to bemounted to the rotor element of FIG. 1;

FIG. 6 is a rear view of the counterweight balancing ring of FIG. 5showing the integrally formed means for securing the balancing ring tothe rotor element; and

FIG. 7 illustrates a tool inserted into a slot machined in a weightedend of a counterweight balancing ring to position the balancing ring ina balance position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Referring now to the drawings, FIGS. 1 and 2 illustrate an annular rotorelement 10 having an axis 12 and a row of scallop shaped locating slots14 about its inner circumference. The rotor element 10 contains twoinner circumferential grooves 16 and 18. Positioned within each of thecircumferential grooves is an annular counterweight balancing ring 20and 22. Each of the counterweight balancing rings 20 and 22, as shown inFIGS. 3-6, has a split ring construction wherein a first end is spacedfrom a second end when said ring is in a relaxed state with the secondends of each balancing ring preferably having a weighted portion 24 and26, respectively. Each ring 20 and 22 also has a plurality of teeth 23for engaging the slots 14.

Each of the counterweight balancing rings 20 and 22 is rotatable withinthe circumferential grooves 16 and 18 when not engaged with one or moreof the locating slots 14. To facilitate its proper positioning, thebalancing ring 20 has a slot 28 machined into its weighted end 24. Theslot 28 may be linear or non-linear. The slot 28 is designed to receivethe end of a tool 44, as shown in FIG. 7, which serves to disengage thebalancing ring 20 from contact with the locating slot(s) 14. The tool 44passes through an opening 46 in an engine casing 48 and through abushing 50 for aligning and holding the tool 44 in place. After the tool44 has been inserted through the opening 46, the rotor is turnedcounterclockwise until the tool 44 bottoms out in slot 28. After thetool 44 disengages the ring 22 from the locating slots 14, the balancingring 20 may be rotated as desired while it is in a disengaged positionby pushing the tool 44 against the end of the slot 28. To facilitate itsproper positioning, the balancing ring 22 has a slot 30 machined intoits weighted portion 26. The slot 30 may be linear or non-linear and isalso designed to receive the end of the tool 44 for disengaging thebalancing ring 22 from the locating slot(s) 14 and rotating thebalancing ring 22 to a desired position.

The provision of the slots 28 and 30 is advantageous for a number ofreasons. First, a slot is inherently less susceptible to failurebecause: (a) there is no overhanging member which can be hung up, aprimary cause of failure, or be acted upon by rotating inertial forces;and (b) the method of manufacture does not require brazing, welding,small radii, or staking, the secondary cause of failure.

Once each of the balancing rings 20 and 22 has been properly positioned,the balancing rings should not rotate relative to the rotor element 10.To prevent such rotation, each of the balancing rings 20 and 22 isprovided with two spaced apart anti-rotation members 40 and 42. Theanti-rotation members 40 and 42 are integrally formed on the rear orinner surface of front balancing ring 20 and on the forward or innersurface of the rear balancing ring 22 and project inwardly to engage twoof the locating slots 14. Each of the anti-rotation members 40 and 42preferably is provided with large fillet radii to enhance its engagementwith a locating slot 14. The engagement between the anti-rotationmembers 40 and 42 on each balancing ring 20 and 22 and the locatingslots 14 helps prevent movement of the balancing rings 20 and 22 duringuse. When the balancing rings 20 and 22 are positioned on the rotorelement 10, the anti-rotation members 40 and 42 on the balancing ring 20occupy two locating slots 14 and the anti-rotation members 40 and 42 onthe other balancing ring 22 occupy two different locating slots 14. Whenthe balancing rings 20 and 22 are to be repositioned, insertion of thetool 44 into the respective slots 28 and 30 causes the anti-rotationmembers 40 and 42 on the balancing rings 20 and 22 to disengage from thelocating slots 14 in which they are seated, thus allowing rotation ofthe balancing rings 20 and 22 to a new position.

While it is preferred to provide two anti-rotation members 40 and 42 oneach of the balancing rings 20 and 22, the balancing rings could havemore than two anti-rotation members if desired.

As previously mentioned before, the locating slots are disadvantageousin that they create aerodynamic windage. To reduce the aerodynamicwindage effects, in a preferred embodiment of the present invention,each balancing ring 20 and 22 is configured or shaped to cover thescalloped shaped locating slots 14 either fully or partially. Ifdesired, only one of the balancing rings 20 and 22, in particular therear balancing ring, may be used to cover the locating slots 14.

In many jet engines, the rotor element has two rows of locating slots.By eliminating one of the rows, as in the present invention, windagelosses are reduced and overall efficiency is improved. A 0.5%improvement in fan efficiency can be achieved merely by reducing one ofthe rows of locating slots. Enclosing the locating slots 14 with atleast one of the balancing rings, also helps reduce windage losses andimprove overall efficiency.

The new counter weight balance technology employed in the presentinvention reduces manufacturing costs due to the ease of machining andthe reduction from two engagement rows as opposed to one row. Further,the use of integrally formed anti-rotation members to secure thebalancing rings in place means that there is no possibility of looseparts, thereby improving durability. Still further, the anti-rotationmembers 40 and 42 provide significant structural advantages which arenot possible with a pin attached to a ring.

It is apparent that there has been provided in accordance with thepresent invention a rotor trim balancing system which fully satisfiesthe objects, means, and advantages set forth hereinbefore. While thepresent invention has been described in the context of specificembodiments thereof, other variations, alternatives, and modificationswill become apparent to those skilled in the art having read theforegoing description. Therefore, it is intended to embrace suchvariations, alternatives, and modifications as fall within the broadscope of the appended claims.

What is claimed is:
 1. A rotor balancing system for turbomachinerycomprising: a rotor element having a row of locating slots; means forreducing windage effects caused by said locating slots; said windagereducing means comprising at least one balancing ring secured to saidrotor element which at least partially covers said locating slots toreduce windage effects; said at least one balancing ring havinganti-rotation means for positioning said at least one balancing ringwith respect to said rotor element; and said anti-rotation meanscomprising two integrally formed anti-rotation members on an innersurface of each said at least one balancing ring for engaging two ofsaid slots.
 2. A rotor balancing system for turbomachinery comprising: arotor element having a row of locating slots; means for reducing windageeffects caused by said locating slots; said windage reducing meanscomprising at least two balancing rings secured to said rotor elementwhich at least partially cover said locating slots to reduce windageeffects; each of said balancing rings having anti-rotation means forpositioning said balancing rings with respect to said rotor element; andsaid anti-rotation means comprising two integrally formed anti-rotationmembers on an inner surface of each of said balancing rings and each ofsaid anti-rotation members being positioned within a respective one ofsaid locating slots to secure each of the balancing rings in positionwith respect to said rotor element.
 3. A rotor balancing system forturbomachinery comprising: a rotor element having a row of locatingslots and a first annular groove; a first balancing ring positionedwithin said at least one annular groove; and said first balancing ringhaving two integrally formed anti-rotation members on an inner surfacefor engaging said row of locating slots.
 4. A rotor balancing systemaccording to claim 3, further comprising: said rotor element having asecond annular groove; a second balancing ring positioned within saidsecond annular groove; and said second balancing ring having twointegrally formed anti-rotation members on an inner surface for engagingsaid locating slots.
 5. A rotor balancing system according to claim 3,wherein said rotor element has only a single row of locating slots.